Blended Families: Recipe for Sibling Rivalry?

Beyond navigating typical sibling rivalry that exists in any family, some parents with adopted and biological children must also consider the challenges that come with so-called blended families.

Much of the tension, however, results not from the children's behavior but that of their parents, several adoption experts told ABCNEWS.com.

"If you have parents who say, 'Look, this is how our family came to be,' the kids will accept it," said Allan Josephson, professor of child and adolescent psychiatry at the University of Louisville School of Medicine. "Parents really set the tone [for the kids]."

Actress Angelina Jolie is perhaps one of the most notably recent figureheads of a blended family. Having first adopted son Maddox from Cambodia in 2002, Jolie has since added to her entourage, adopting daughter Zahara from Ethiopia in 2005, giving birth to daughter Shiloh in 2006 and then last year adopting son Pax from Vietnam.

And four wasn't enough: Jolie is expecting twins this August with boyfriend Brad Pitt.

After she gives birth this summer, Jolie will have six children — three biological kids and three whom she has adopted.

Adoption experts told ABCNEWS.com that the relationships these children will have with one another — and whether there will be resentment or jealously — may not have much to do with the children at all, and could hinge almost entirely on the way their parents act toward them.

Kids' Relationship Depends on Parents' Fairness

"The main thing that leads to success is the commitment of parents that these children are theirs, no matter how they were conceived," said Josephson, who is also the CEO of the Bingham Clinic that specializes in child psychiatry. "And if they're adopted at infancy these types of blended families can almost have no differences when compared with biological families."

"[Adoption] is just a fact that [the children] are informed of," said Josephson, adding that it's important for adopted and biological kids to have the same legal last name, rights and privileges as one another so parents do not appear biased toward one child over another.

"The relationship between the kids all stems from the parent — if the parent has been evenhanded with the children, the kids will accept their situation," Josephson said.

Josephson said that while society's stigma about adoption may lead some to believe that blended families experience the most problems among siblings, he suspects that the familial relationships between step-siblings or half-siblings are even worse.

"Biological and adoptive combinations are always easier than a blended family that resulted from a set of failed or broken families," Josephson said. "The dynamics in those situations are very difficult in the sense that the children aren't all 'owned' by the same parents."

Child psychiatrists and author of "Raising Kids With Character" Elizabeth Berger told ABCNEWS.com that how parents act not only toward their kids but also toward each other matters tremendously to the relationship their children foster.

"Nasty situations are often indicative of a dynamic that really involves the whole family," Berger said.

Adopted or Not, Kids Will Be Kids

Barbara Taylor Blomquist had already given birth to a baby girl when, three years later, she decided to add to her family — the less conventional way.

Adopting two infant boys within three years of one another, Blomquist told ABCNEWS.com that her children never had any animosity toward one another because of the adoption, and their problems were rooted in who they were as individuals and how they related to one another.

"I think the general public sees adopted children as causing more problems within families than biological ones do, and sometimes that is the case but often it's not," said Blomquist, who wrote the book "Insight Into Adoption," which stems from her experience as an adoptive mother.

"Each time we adopted a baby boy, it was our daughter's little baby brother," Blomquist said. "When you're growing up, children are children."

The problems many adopted kids have to deal with are certainly important to recognize, said Adam Pertman, executive director of the Adoption Institute and author of "Adoption Nation," who went on to say that they may not be any worse than other problems families face.

"There are a lot of blended families that bring together different sorts of kids and do just fine," Pertman said. "They bring their own challenges and sometimes there are issues and sometimes not, but there's nothing particularly special about adoption in this respect. It just has its own particular dynamic."

"Are there complexities and differences? Of course there are," Pertman said. "The complexities are inherent — one sibling looks like you and another does not."